Space based gravitational wave sensors rely on position measurements of proof masses to sense gravitational waves. Since the effects of gravitational Waves are extraordinarily small, it is important to minimize all other forces on the proof masses. Accumulation of a net electric charge on a proof mass can result in spurious forces on the proof mass (e.g., a Lorentz force from motion through the interplanetary magnetic field, and/or electrostatic forces from other bodies with a net or induced charge). Accordingly, proof mass charge management to eliminate net electric charge on the proof mass is important. The standard approach for performing proof mass charge management relies on the photoelectric effect induced by UV radiation from a UV source. Present instrument designs employ Hg lamps in the UV source.
However, this approach for proof mass charge management is unsatisfactory in several respects. First, Hg lamps are: physically large, mechanically fragile, sensitive to temperature variations, significant sources of EMI and RFI, and consume a large amount of power in operation, all of which are highly undesirable in space applications.
Second, it can be difficult to obtain the dynamic range required in practice. For example, in one space mission, the nominal discharge rate is on the order of 10s to 100s of electrons/s, but discharge rates on the order of 1 to 10 million electrons/s can be required after initial release of the proof mass or after it makes contact with another object. Since Hg lamps typically have a dynamic range on the order of 10-100, several lamps having varying output power ranges may need to be included in the UV source to cover a mission dynamic range of about 100,000. The use of several lamps in the UV source further increases the above-identified problems associated with Hg lamps.
The photoelectric effect has also been employed for charge management in connection with other applications. For example, in U.S. Pat. No. 6,545,853, the photoelectric effect is exploited to provide a spacecraft ground. In U.S. Pat. No. 5,898,268, the photoelectric effect is exploited to provide neutralization of accumulated positive charge on a semiconductor wafer by illuminating a photocathode disposed near the wafer.
Another example of charge management is considered in US 2004/0027777, where UV light emitting diodes are employed for eliminating static electricity from a target via emission of photoelectrons from the target and/or by ionization of gas molecule around the target.
However, these non-sensor applications of charge management do not appear to require a high dynamic range of the charge transfer rate. Accordingly, it would be an advance in the art to provide charge management having a high dynamic range.